Many oil wells are initially naturally pressurized to cause the oil to flow to the surface. Later, many wells must be pumped to remove the oil from the subsurface formation. In such cases, a pump jack has typically been used to pump the liquid from the well. In many cases, as the oil is withdrawn, water begins to take its place and the pump jack begins to pump both oil and water. Some patented systems have proposed use of valves at the bottom of the oil well to close the valve when water is present so that water is not pumped from the well. Such systems are shown in U.S. Pat. Nos. 2,762,437 and 3,018,828. Another patented system is shown in U.S. Pat. No. 3,915,225, wherein the pump is turned off when the water level rises to the bottom of the well tubing in the well. U.S. Pat. No. 3,559,731 disclosed control of a pump jack which pumps off the well until there is inadequate flow. Then, after a first timer times out, the pump motor is de-energized. A second timer restarts the pump motor, but will shut down after a time period of the first timer unless there is adequate pump flow.
The typical experience in oil fields is to have short-cycle pumping, wherein the pump jack is operated for a short period of time to pump out the liquid in the oil well, and it may then be separated at the surface between oil and water. The oil well pumping is shut down periodically in order to permit the liquid to again fill up the reservoir in which the well casing is located. Since each well is different and presents different problems, a set time-on and time-off period for the individual pump jacks becomes quite difficult to determine, and each must be set individually and then can change with time as the oil is depleted from the underground formation. This has resulted in the pump jacks not operating for a sufficient length of time to pump off the well fluid, so that it is not an economical production from the well or, alternatively, the pump is operated for too long a time and the well is pumped off, pumping out all the liquids. This is even worse on the mechanical equipment because then the pump rods are subjected to pounding, and it has been observed that this is when most mechanical failures occur. It is also uneconomical to continue operation of the pump when no liquids are being pumped from the well.
U.S. Pat. Nos. 3,559,731 proposes a circuit to shut off the motor driving the pump jack when pump-off of the well occurs, but the control circuit is one which establishes high voltage at the well head, which could be a personnel hazard, and the circuit has limited interface with existing well head equipment. Additionally, there is no lockout feature to lock out the motor starter if there should be a malfunction in the pumping equipment, and thus cycling of the pump motor on and off will occur. Also, if there is a power failure to the electrical control circuit, the pump motor will be allowed to run continuously. In such circuit, a number of relay contacts are provided and failure or burnout of such contacts will allow the pump motor to run continuously. Should some fault occur due to failure of the circuit or circuit components, the entire circuit does not allow for pumping the well by conventional timing means. The commercially available pressure or flow sensing devices used in that circuit, especially in the northern climates, are not immune to freeze-up or paraffin buildup. Such circuit provides no means for recording the performance of the well, such as the time of pumping water and of pumping oil. That circuit provides no visual indication that well shutdown has occurred due to problems as distinguished from shutdown due to natural pump-off of the well. Also, if a fault should occur in that prior art circuit, due to failure of the relay coil of the first timer, continuous pumping of the well occurs, and such timer coil is energized during the entire time of flow of liquid from the well. Further, it is common to have more than one well pumping into a collection line and where the prior art circuit utilizes a pressure switch, then this also requires a check valve, and failure or leakage of such check valve will maintain the pump motor energized, with a second pump pumping into the same collection line.